> ## Documentation Index
> Fetch the complete documentation index at: https://docs.zapier.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Message availability notification

> Sent to the inbox's notification_url when new messages are available to lease. The payload signals availability only — it does not include message content. Consumers should call the lease endpoint to retrieve messages.



## OpenAPI

````yaml /api-reference/specs/trigger-inbox.yaml webhook messageAvailable
openapi: 3.1.0
info:
  title: Trigger Inbox API
  description: >-
    Manage trigger inboxes and their messages — create, pause, resume, and
    delete inboxes; list, lease, and acknowledge messages.
  version: 1.0.0
  contact:
    url: https://docs.zapier.com
servers:
  - url: https://api.zapier.com
    description: Production
security:
  - OAuth: []
tags:
  - name: Inbox Messages
    description: Lease, acknowledge, and release inbox messages
  - name: Inboxes
    description: Create and manage trigger inboxes
paths: {}
components:
  securitySchemes:
    OAuth:
      type: oauth2
      description: OAuth 2.0 authentication.
      flows:
        authorizationCode:
          authorizationUrl: https://zapier.com/oauth/authorize
          tokenUrl: https://zapier.com/oauth/token
          scopes:
            external: Scope that gives access to all Public APIs
        clientCredentials:
          tokenUrl: https://zapier.com/oauth/token
          scopes:
            external: Scope that gives access to all Public APIs

````